Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$62.27	6.443%	$66.2821	$66.28	$66.30	$66.30
Purchase #2	$127.84	9.772%	$140.3325	$140.33	$140.35	$140.30
Purchase #3	$129.62	10.291%	$142.9592	$142.96	$142.95	$143.00
Purchase #4	$237.85	7.658%	$256.0646	$256.06	$256.05	$256.10
Purchase #5	$80.43	12.629%	$90.5875	$90.59	$90.60	$90.60
Purchase #6	$84.31	12.730%	$95.0427	$95.04	$95.05	$95.00
Purchase #7	$87.76	9.575%	$96.163	$96.16	$96.15	$96.20
7 purchase totals =	$810.08		$887.4316	$887.42	$887.45	$887.50